1. Field of the Invention
The present invention relates to the treatment of shale oil for the removal of trace metals therefrom, in particular, arsenic, iron and nickel, using a particular alumina contact structure.
2. Related Art
Shale oils produced by the various retort systems contain small amounts of metal contaminates, which in so far as further processing or use are detrimental. For example, further treatment of the shale oil crudes in the various catalytic refinery processes containing the metal contaminates can substantially shorten the life of the catalyst. Serious environmental hazards can also arise if, for example, the arsenic is not reduced to the lowest possible levels.
The removal of arsenic and other trace metals has been proposed by several methods. Generally, these are heat soaking or visbreaking, catalytic contact, and thermal treating in non catalytic packing.
Heat soaking involves heating the oil long enough to form a suspended precipitate which must be subsequently separated by mechanical means.
Catalytic methods involve contacting the shale oil with a catalyst such as oxides or sulfides of nickel, cobalt or iron at elevated temperatures and usually under partial hydrogen pressure.
Thermal treating involves contacting the oil with a non catalytic packing with or without partial hydrogen pressure to deposit all or a portion of the trace metal contaminates on the packing.
Numerous variations of these procedures and various combinations have been proposed for demetallization of carbonaceous oils, including shale oil to obtain safe and industrially acceptable amounts of the metals.
Several patents have been issued on the demetallization of shale oils and other liquids. U.S. Pat. No. 4,046,674 describes a process for specifically removing As from mineral oil feedstocks containing at least 2 ppm As by reacting the oil at 450.degree.-700.degree. F. and 50-5000 psig in the presence of H.sub.2 with a catalyst consisting of 30-70% NiS of MoS.sub.2 on a refractory oxide. This patent teaches removing at least 1.5 pounds of As per pound of metal on the catalyst.
U.S. Pat. Nos. 3,804,750; 3,876,530; 3,876,533; 3,898,155; 3,954,603; 4,003,829; 4,051,022; and 4,212,729 all disclose removing metals (some disclose removing As specifically and some mention only V, Ni and Fe as they relate to heavy residual demetallization) from various oils using aluminas loaded with at least one of Ni, Mo, Mn or W.
U.S. Pat. No. 4,188,280 discloses removing soluble As and Fe compounds from shale oil with or without added H.sub.2 with a porous solid contact material at 149.degree.-510.degree. C. and 50-3000 psig total pressure. This patent discloses reducing As and Fe levels both to less than 1 ppm from shale oils containing more than 4 ppm soluble As and 10 ppm soluble Fe.
U.S. Pat. No. 3,933,624 discloses that As and Fe specifically can be removed from synthetic oils by mixing the crude oil feed with particles of either Fe, Co, or Ni in the form of oxides or sulfides in the presence of H.sub.2 at 300.degree. F. and 500 psig. This forms a slurry which is removed from the oil.
U.S. Pat. No. 4,029,571 discloses that As can be removed from synthetic oils by heating to 750.degree.-850.degree. F. forming a precipitate which is then filtered.
U.S. Pat. No. 4,075,085 discloses that As can be removed from hydrocarbon feedstocks by mixing oil with oil-soluble Ni, Co or Cu-containing additives at 300.degree. F., forming an As-containing precipitate which is then filtered.
U.S. Pat. No. 4,141,820 discloses the removal of arsenic from hydrocarbon oil using a solid refractory oxide of a group II, III, or IV element of the Periodic Table, by contacting the oil and hydrogen gas with the solid at 200.degree. to 500.degree. C., the solid having a surface area of 10 m.sup.2 /gram or more and pore size of about 40 Angstroms to 1000 Angstroms.
An examination of the volume of art in this general area will show very little concern, if any, is directed to the particular form of the contact structure (catalytic or non-catalytic). For example, in U.S. Pat. Nos. 3,804,750 and 4,051,022 the catalyst is taught to be in any physical form, including powders, pellets, granules, spheres, flakes, cylinders, and the like; in U.S. Pat. No. 4,075,085 a packing material is taught to be alundum balls, quartz chips, siliceous gravels, alumina pellets, Rashcig rings and the like; U.S. Pat. No. 3,876,533 teaches the guard bed is composed of pellets or particles of any shape; and U.S. Pat. No. 4,046,674 teaches a catalyst which is extruded as a trilobe.
Bruijn, Naka and Sonnemans investigated the effect of catalyst shape of extruded hydrodesulfurization catalyst in "Ind. Eng. Chem. Process Des. Dev.", 1981, Vol. 20, No. 1, pages 40-45. Their conclusion was that the activity of noncylindrical extrudates may be higher than cylindrical particles because it permits the use in the catalyst bed of smaller particle size at an equal pressure drop.
It is an advantage of the present invention that over 90% of arsenic and iron may be removed from crude shale oil. It is a further advantage that either hydrogen or nitrogen or neither may be present during the process to produce excellent results. It is a feature of the present invention that the contact material which provides such superior removal of arsenic and iron (and nickel to a lesser extent) also provides low pressure drops in the reactor and excellent flow characteristics. These and other advantages and features will beome apparent from the following description.